The capacity of rechargeable and non-rechargeable batteries is defined by the positive cathode and the negative anode. When using a metallic lithium anode (e.g. in Li—MnO2 coin cells) or a capacity rich Li-ion anode that, for example, may be based on silicon or tin, the capacity of the battery is dominated or limited by the specific capacity (measured in mAh/g or mAh/ccm) of the positive cathode. Reducing the volume of all of the other battery components, which is most useful for small batteries, or the mass of all of the other battery components, which is most useful for large batteries (e.g. in electric vehicles), while simultaneously increasing the electrochemically active mass inside the positive cathode is the most effective approach to increase the energy density (measured in Wh/liter, for example) of a battery for a given cathode-anode chemistry.
Increasing the electrochemically active mass inside the positive cathode means to either reduce any auxiliary phases inside the cathode, such as mechanical binders or ionic or electronic conduction enhancers, or fabricate the cathode thicker for a given cathode area. Due to the limiting diffusion kinetics and the associated limited current rate or power capability when the cathode thickness becomes substantial (>>20 μm), high energy density room temperature batteries, such as cell phone and laptop batteries, require a highly conductive, liquid-organic-solvent based lithium ion electrolyte to penetrate the cathodes of these batteries. However, the presence of the liquid organic solvent is the origin of most problems experienced with such batteries over the last twenty years such as, for instance, thermal runaway upon decomposition or short-circuiting of the battery upon heat-related failure, fire/fume/smoke/explosion upon certain battery failure modes, gas evolution and pressure build-up in the early electrochemical cycles, charge-discharge cycle limitation to 300-1000 cycles, limited operational temperature range (0° C.-60° C. in many cases), among others. In addition, constraining the volatile liquid organic solvent demands specific packaging architectures and cell housing often equipped with vents and valves that avoid cell over-pressurization during the early electrochemical cycles.
There is a need in the industry for batteries with higher energy densities. In particular, there is a need for all-solid-state rechargeable batteries without any liquid or gel-type battery components to store more energy in a limited volume that still show acceptable power and/or current rate capability. This results in a safer battery and allows for the use of simplified packaging and higher and lower temperature ranges of operation and storage.